1. Field of the Invention
The present general inventive concept relates to a backlight unit of an edge light type, and more particularly, to a backlight unit improving non-uniformity of brightness due to the disposition and the shape of a light source, and increasing a light efficiency thereof.
2. Description of the Related Art
In general, a liquid crystal display apparatus, as one of a light receiving type display apparatus, is incapable of emitting light by itself. Thus, the liquid crystal display apparatus forms an image using an illuminating light emitted from the outside. For this, a backlight unit to illuminate a light is disposed at a rear surface of the liquid crystal display apparatus.
A backlight unit may be classified as a direct light type or an edge light type. In the direct light type, a lamp disposed directly under a liquid crystal panel directly emits light upward to the liquid crystal panel. In the edge light type, a lamp disposed at an edge of a light guide panel (LGP) emits a light, and the emitted light is transmitted to the liquid crystal panel through the light guide panel.
FIG. 1 is a schematic sectional view illustrating a conventional backlight unit of the edge light type.
As illustrated therein, a cold cathode fluorescent lamp (hereinafter, referred to ‘CCFL’) 3, and a reflecting mirror 5 reflecting light emitted from the CCFL 3, are disposed at opposite edge parts of a light guide panel (hereinafter, referred to ‘LGP’) 1. Also, a reflecting sheet 7 is formed on a lower surface of the LGP 1. The reflecting sheet 7 reflects light entering from the CCFL 3 toward the liquid crystal panel. Accordingly, the light emitted from the CCFL 3 enters the LGP 1 through an edge. This entering light is converted into a surface light by means of the reflecting sheet 7 to be emitted to an upper surface of the LGP 1.
Also, an optical sheet 9 correcting a proceeding path of the emitted surface light is provided at an upper surface of the LGP 1.
The quantity and length of the CCFL 3 are determined according to a standard of the LGP 1. The CCFL 3 is a line light source provided on at least one side of four sides of the LGP 1.
FIG. 2 illustrates a configuration of the CCFL 3 having an ‘L’ shape, and disposed to illuminate light to all four sides of the LGP 1. In this case, since the CCFL 3 is disposed on all four sides of the LGP 1, a high brightness can be obtained in comparison to the backlight unit having the CCFL which is disposed to only an edge of the LGP 1.
Also, related to the shape and disposition of the CCFL 3, as illustrated in FIG. 2, if two CCFLs 3 of the ‘L’ shape are used, an area A of the backlight unit corresponding to a bent portion of the CCFL 3 receives an exceeding amount of the light to become a bright portion having a high brightness, and a portion B of the backlight unit corresponding to an end part of each CCFL 3 receives an insufficient amount of the light and thus becomes a dark portion having low brightness.
Accordingly, as illustrated in FIG. 2, related to a brightness distribution of the surface light emitted from the LGP 1, the area A is brighter than an area C representing a central part of the backlight unit, and the area B is darker than the area C, so that light having a uniform brightness is incapable of being totally illuminated. In FIG. 2, numbers indicated inside the other areas represent an average brightness value of each respective area, and the unit of measure thereof is candela per meter squared (cd/m2) which is a standard unit of luminance.